Sidebar

your theme is Twenty Eleven with some css adaptations (not much custom blog at all) –

ideally your developer should have created a child theme http://codex.ww.wp.xz.cn/Child_Themes

make sure to make a buckup copy of your theme, and don’t update the theme when you upgrade your wordpress version or you will lose all cusomisations.

for the sidebar problem, try to work with a plugin such as http://ww.wp.xz.cn/extend/plugins/twenty-eleven-theme-extensions/

(remove the code from single.php again)